It’s pointless! It doesn’t mean anything to anyone. The truth is, if one feels inclined to give themselves such a title then it probably isn’t true. It’s also quite uncreative as far as self promotion goes.
If I AM an expert it will be apparent to those that know my work – and if they use the word “expert” to describe my proficiency? Great! But for me, it’s not an attainable (or measureable?) destination. It’s the idea of being on top of your game and being appreciated for it that’s worth striving for.